The present invention relates to systems for controlling the temperature in vehicle passenger compartments and is particularly related to vehicles having a pump or compressor generating a source of refrigerant for circulating to means for cooling the passenger compartment during warm weather. This invention also relates to such systems operating with heating means receiving engine coolant for providing heat to the passenger compartment during cold climate operation.
In providing climatic comfort systems for automotive vehicles, it is commonplace to provide an operator activated manual cooling or air conditioning system for warm weather operation and a separate operator actuated heating system for cold weather operation. In such manual systems, the operator selects a level of system operation and heated or cooled air is discharged from a blower plenum into the passenger compartment. However, for increased occupant comfort and operator convenience, automatic temperature control systems have been provided wherein the operator selects a desired temperature and the system blends a mixture of air blown over the heating means and cooling means and discharges blended air from the plenum to regulate the temperature of the passenger compartment. Such known automatic systems have employed a sensor responsive to the passenger compartment temperature to provide a fluid pressure control signal for determining the position of a blend air door for proportioning the amount of air from the blower directed to the heating and cooling means. Examples of such systems are those described and shown in U.S. Pat. Nos. 3,774,676, 3,983,930 and copending application Ser. No. 50,022 filed June 18, 1979, entitled "Vehicle Temperature Control System", in the name of R. J. Franz, assigned to the Assignee of the present invention.
The known automatic vehicle passenger compartment or cabin temperature control systems provide for continuously circulating engine coolant through the heating means and operating the refrigerant compressor and proportioning air flow from the blower to the heating means and cooling means for obtaining the desired temperature of blended air for discharge to the passenger compartment. Thus, the known automatic vehicle cabin air temperature control systems require that the valve controlling flow of engine coolant to the heating means be operated in the open position continuously, even when the control system requires only cooling of ambient air for occupant comfort. Heretofore, the cooling-only mode in automatic temperature control systems has been accomplished by positioning a blend air door to divert all blower air over the cooling means. Known automatic temperature control system, when operated in the heating only mode, blend cooled air blown over the cooling means with heated air from the heating means in order to obtain the desired temperature of heated air for discharge. The prior art systems thus continued operation of the engine driven compressor for circulating refrigerant to the cooling means even when the system was being operated in the heat only mode.
Consequently, the known automatic vehicle temperature control systems have required the engine to provide the additional power for operating the refrigerant compressor when only heating of the vehicle cabin was desired, with a resultant increase in the fuel consumption of the vehicle engine. At a time when the cost of engine fuel was a minor portion of the operating cost of the vehicle, the increased fuel consumption was considered unimportant in view of the comfort, convenience and desirability of an automatic system for regulating the passenger compartment temperature at a preselected set point. However, where the cost of engine fuel is a major consideration in the operation of the vehicle, it has been desired to provide an automatic temperature control system for the passenger compartment which minimizes the power drain from the engine, thus permitting more of the engine output to be utilized for vehicle propulsion. It has thus been long desired to provide a system which automatically regulates the vehicle passenger compartment temperature in a most efficient manner and yet provides sufficient sensitivity as to respond adequately to variations in the passenger compartment temperature due to ambient temperature variations, number of passengers carried, and solar heat loads.
Heretofore, all automotive air conditioning systems including both the manual type and automatic temperature control systems have employed a pressure sensor in the refrigerant line to the cooling means to sense freezing of moisture condensate on the cooling means. Ice buildup on the cooling means tends to block blower air flow over the cooling means and thus renders the system unable to cool the passenger compartment.
Previous attempts to prevent energy waste in automatic vehicle passenger compartment temperature regulation have employed the techniques of varying the bias on the refrigerant pressure sensing switch to produce on and off cycling of the refrigerant compressor in response to variations of the pressure in the refrigerant line to the cooling means. An example of this type of a system is that described in the aforementioned commonly assigned application, Ser. No. 050,022. However, the aforesaid system, although providing an in-car temperature sensor to control cycling of the refrigerant compressor, nevertheless required that the engine coolant valve to the heating means be open when the system was operated in the cooling only mode, since the primary control of cabin air temperature was accomplished by positioning a blend air door for mixing air blown over the cooling means and the heating means. Thus the aforesaid prior art system required expenditure of energy to provide refrigerant air cooling and then reheating of the cooled air for temperature regulation.
Therefore, it has long been desired to provide an automatic system for regulating vehicle passenger compartment temperature, yet provide such a system which does not require the operation of the refrigerant compressor, even on a modulated duty cycle basis, during cold climate vehicle operation when the temperature control system is operated in the heat-only mode. It has also been desired to provide a simplified automatic temperature control system for vehicle passenger compartments in which freezing of condensed moisture on the cooling means could be prevented by control sensitivity during normal operation. Further, it has been desired to provide such a system having control of moisture condensation freezing on the cooling means in a manner which does not require separate sensors and complete cut-out of the refrigerant compressor for prolonged periods.